1. Field
This invention relates to efficient recovery of energy in an AC-to-AC power inverter system. More particularly, it relates to an efficient bi-directional circuit configuration with load stability for a power source inverter system.
2. Background
It is common, for more sophisticated power systems that use three (3) phase AC line inputs, to implement a set of six (6) input switching bidirectional inverters that flatten the input AC to a DC value. The DC is supplied to a bus that is coupled to six (6) output switching inverters which then convert the DC back to AC. This AC-to-DC and from DC-to-AC path provides needed output voltage stability and input isolation, particularly when the input source is a “fluctuating” AC grid or if the load requires very stable power.
More advanced systems allow for power to be transferred back into the input AC grid when the DC-bus voltage exceeds the normal input line voltage, via the input bidirectional inverters. Due to all the switching and circuit losses, the normal efficiency of these systems is around the low 90%. In addition to these losses, these systems require a very large DC-link capacitance bank to compensate for step-wise load variations (e.g., switching on an electric motor) that would otherwise cause unacceptable voltage/current fluctuations.
In view of the above, there has been a long-stand need in the industry for inverter systems that have higher efficiencies and are less sensitive to step loads. Solutions to these and other shortcomings in the power inverter industry are elucidated in the following description.